Researchers pull sleds with camera gear and other equipment to a polar bear den site

Photo: Kt Miller / Polar Bears International

The research team pulls sleds with camera gear and other equipment to a polar bear den site. The non-invasive study records the behavior of moms and cubs after they emerge from their dens to better understand the denning process.

Q&A: Svalbard Maternal Den Study

By Barbara Nielsen, Director of Communications



01 Feb 2024

Every year, one of our research teams spends three weeks in Svalbard, Norway, where they take part in a maternal den study in partnership with the San Diego Zoo Wildlife Alliance and the Norwegian Polar Institute. The study involves placing remote cameras at den sites to record the activity of emerging polar bear moms and cubs. A related pilot project is testing whether radar can be used to detect polar bear dens hidden under the snow. 

We caught up with Geoff York, our senior director of science and policy, to learn more about the projects and why they matter.

Q: First, could you tell us a little about polar bear moms and cubs in their dens?

A: It’s actually quite remarkable. Female polar bears dig dens in snow banks in the fall and give birth to their cubs in late December or early January—a time of year when temperatures outside can plunge to -40. At birth, the cubs are blind, covered with light fur, and weigh roughly one pound. The cubs are quite vulnerable at that stage. They rely on their mother’s care and the shelter of the den for their survival. The family remains in the den for three or four months, hidden from view, until the cubs are strong enough to follow their mom to the sea ice in spring.

The inside of a polar bear den

Photo: BJ Kirschhoffer / Polar Bears International

The inside of a polar bear den, after the family has departed. Note the claw marks on the den walls.

Q: This research project focuses on the time period when the family breaks free of the snow den in spring. What do you hope to learn?

A:  Sea ice loss due to climate change is impacting denning polar bears across the Arctic. In the Barents Sea—where sea ice loss is most dramatic—we are observing fewer maternal dens on Svalbard, as well as moms and cubs in poorer condition when they emerge from their dens. This issue could worsen as an ever-warming Arctic opens new opportunities for tourism and development in the North.

Unfortunately, very little is known about polar bear denning behavior—and even less is known about the impacts of human disturbance on denning bears. This project will help answer those questions, so wildlife managers can better protect moms and cubs.

Q: What does the study involve?

A:  We monitor dens with small solar-powered camera systems that have been refined over years of field testing. The cameras are built to withstand harsh Arctic conditions and are placed remotely to avoid disturbing denning families. We set up the cameras while the bears are snug in their dens, hidden under the snow—and then we depart, leaving the cameras to do the work.

When the family emerges from their snow den in spring, the cameras capture their activity. The footage allows us to assess the body condition of the moms and cubs. It also provides information on how families spend their time and how long they remain at the den site before heading to the sea ice to hunt seals.

It’s a non-invasive study. We return to retrieve the footage and the equipment after the bears have left their den.

Researchers set up a camera and solar panels near a polar bear den site

Photo: Kt Miller / Polar Bears International

The research team sets up a camera and solar panels near a polar bear den site. From left to right: BJ Kirschhoffer of Polar Bears International and Joanna Sulich and Marius Nyborg of the Norwegian Polar Institute.

Q: When did you start the project?

A: We started the Svalbard study in 2016, building on earlier den study work that we did in Alaska as part of a project led by Dr. Tom Smith of Brigham Young University. It was originally launched by the USGS. That work was motivated by the fact that more and more industrial activity was moving into the region, yet little was known about denning behavior and what impact it might have.

Since that early work in Alaska, our systems have changed greatly. The cameras are so small and energy-efficient now that our packages have shrunk from 300 pounds (and quite bulky!) to the size of a carry-on suitcase weighing about 35 pounds. They’re so compact and easy to transport that they could be sent to any denning area, from Greenland to Russia to Canada and Alaska. What’s more, they can easily be set up by anyone after some fairly basic training.

Q: How many dens do you typically monitor each year?

A: That varies based on the number of known den locations and their accessibility, but we generally place cameras at two to five den sites each year. Because polar bears on Svalbard den on steep mountain slopes, sometimes the only way to reach them is by helicopter, landing a safe distance away. After landing, we usually ski in with our equipment, but one year there was almost no snow so we mostly hiked in from there, pulling the sled with our equipment.

This year our team includes myself; Joanna Sulich, one of our consulting scientists; Christian Zoelly, our director of field operations and logistics; and partners from the San Diego Zoo Wildlife Alliance.

Q: Are there any differences between the study in Svalbard and the previous project in Alaska?

A: There are quite a few differences, starting with terrain. Along the North Slope of Alaska, the landscape is mostly flat with subtle features—almost like being on the moon! Also, there is quite a bit of oil and gas activity in the central region. Svalbard, on the other hand, is characterized by steep mountain slopes, glaciers, crevasses, and dramatic fjords. No industrial activity takes place in the denning areas, but snowmobilers and skiers visit the more accessible slopes. So, the types of human activity in the two regions are quite different, as are the denning conditions for the bears.

Q: What have you learned so far?

A: As you can imagine, we have weeks of footage to analyze every year. When we started the study in 2015, a colleague at the San Diego Zoo Wildlife Alliance logged the footage. But that was incredibly time-intensive, so in 2021, we worked with a San Diego Zoo programmer on a machine-learning system that can go through all the data in a short amount of time, logging where there is footage with polar bears in it.

After we know where to look, Joanna Sulich, who is based in Svalbard, analyzes the logged footage, recording metrics such as the number of cubs, the health and body condition of both moms and cubs, their behavior around the den site, and how long they hang around the den before departing for the sea ice. We now have enough data to publish results and, in fact, are working on a paper that we plan to publish later this year. 

Among our findings, aside from metrics, we’ve documented that polar bear moms emerge from their dens earlier than indicated by collar data. Additionally, before the family emerges from the den, polar bear moms begin peeking out of the den for short periods of time. After the mom heads outside, her cubs follow, but only on warmer days, and they remain close to the den. After the cubs begin emerging more often, and presumably start feeling more comfortable with their surroundings, they start to increase the distance from the den and their mother.

Snow-covered mountain in Svalbard

Photo: Kt Miller / Polar Bears International

Svalbard's steep mountain slopes serve as denning sites for polar bears, terrain that is quite different from den locations in northern Alaska.

Q: What about the related den-detection project? Any findings yet?

A: We are testing two different types of radar to see if they can find dens under the snow. One is synthetic aperture radar, or SAR, which can be mounted to a small aircraft, a project in partnership with Brigham Young University and Simon Fraser University. The other is a wide-band radar that can be mounted to a drone, a project in partnership with the Norwegian Polar Institute and NORCE. While both methods appear promising, more work needs to be done. Developing technology to pinpoint den locations is needed in order to protect polar bears from human activity, as the current method used, FLIR, misses more than half of known dens.

We tested SAR in Svalbard in 2022 and the wide-band radar in 2023. This year, if the weather and logistics permit, we plan to test the ability of the wide-band radar to detect an unoccupied dens. Future plans call for testing both in Alaska, where more human activity takes place and where the terrain is quite different from the steep slopes of Svalbard.

Q: Why does it take so long to learn anything from studies like these?

A: When studying behavior like denning, long-term studies are important because we are looking at an animal with a long lifespan. If we look at just one, two, or five years of a bear’s life, we get a very incomplete picture. Polar bears could have low—or high—birth rates for several years in a row, then completely reverse for the following 10 years. Polar bears require what we call a longitudinal study lest we make premature conclusions about them. The same holds true for monitoring the family’s body condition, the number of cubs, and so on. You need a long data set.

With the den-detection work, you also need a robust data set, under different conditions and on different terrain, to fully assess the effectiveness.

Q: What are your future plans for the project?

A: We plan to continue with this research in Svalbard, a part of the Arctic with rapid environmental change. A long data set there will provide critical information on the impact of these changes on moms and cubs. In addition, we are considering expanding the study to other areas, including Canada and Alaska. 

Q: Is there anything else you’d like to add?

A: In Svalbard, we are constantly surprised about where the bears choose to den. To anyone who knows snowy mountains and the danger of steep slopes and avalanches, it’s amazing to see how frequently the bears perch themselves in fairly precarious places. For a cub coming out of the den for the first time, he’d better know how to use his brakes! It’s remarkable how polar bear moms have figured out how to den on these steep slopes and then lead their young cubs to the sea ice. The more I learn about polar bears, the more amazed I am.